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| LMH6624_16 Datasheet, PDF (20/38 Pages) Texas Instruments – LMH6624 and LMH6626 Single/Dual Ultra Low Noise Wideband Operational Amplifier | |||
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LMH6624, LMH6626
SNOSA42G â NOVEMBER 2002 â REVISED DECEMBER 2014
Feature Description (continued)
7.2.3 Noise Figure
Noise Figure (NF) is a measure of the noise degradation caused by an amplifier.
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(5)
The Noise Figure formula is shown in Equation 5. The addition of a terminating resistor RT, reduces the external
thermal noise but increases the resulting NF. The NF is increased because RT reduces the input signal amplitude
thus reducing the input SNR.
2 22
2
en + in (RSeq + (Rf||Rg) ) + 4KT (RSeq + (Rf||Rg))
NF = 10 LOG
4KT (RSeq + (Rf||Rg))
(6)
The noise figure is related to the equivalent source resistance (Rseq) and the parallel combination of Rf and Rg.
To minimize "Noise Figure":
⢠Minimize Rf || Rg
⢠Choose the Optimum RS (ROPT)
ROPT is the point at which the NF curve reaches a minimum and is approximated by:
ROPT
»
en
in
(7)
7.2.4 Low Noise Integrator
The LMH6624 and LMH6626 devices implement a deBoo integrator shown in Figure 52. Positive feedback
maintains integration linearity. The low input offset voltage of the LMH6624 and LMH6626 devices and matched
inputs allow bias current cancellation and provide for very precise integration. Keeping RG and RS low helps
maintain dynamic stability.
VO #VIN KO
sRSC
RF
; KO = 1 +
RG
RB
RS
VIN
C
+
R
-
RF
VO
50:
50:
RF = RB
RG
RG = RS||R
Figure 52. Low Noise Integrator
20
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Product Folder Links: LMH6624 LMH6626
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